Single-ion transfer energetics in some aqueous alkanols and the structuredness of aquo-organic solvents

Abstract

Single-ion transfer energetics of some ions based on the widely used tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption have been determined in aqueous mixtures of 10, 20, 30, 50 &amp; 70 wt% alkanols like ethanol (EtOH) and 2-propanol (2-PrOH) from solubility measurements of KPi, Ph₄AsPi, KPh₄B and Ph₄AsI [Pi-picrate, Ph = phenyl] at five equidistant temperatures in the range 15-35&deg;C. Transfer free energies, &Delta;G<em>&nbsp;</em>(i), of the ions in aqueous EtOH and 2-PrOH as well as those in aqueous mixtures of methanol (MeOH) and z-butanol (t-BuOH), as obtained from the literature, after elimination of cavity effect and Born-type and ion-dipole-type electrostatic interacton effects, helped reveal acid-base typej interaction effect of solvents that dictate transfer chemical free energies of the ions, &Delta;G_{, ch} (i). On the other hand, transfer entropies, <em>T</em>&Delta;S_,ch (i), obtained after due correction of cavity and Born-type electrostatic effects from T&Delta;S<em>&nbsp;</em>(i) values, when analysed in the light of Kundu <em>et al's </em>four-step transfer process as well as the fact that increasing hydrophobicity of the I cosolvents helps increase the 3D-structuredness of these aquo-alkanolic solvents, led us to conclude that entropies of single ions rather than the complete electrolytes, serve as a better structural probe for aquo-organic solvents. This has also been substantiated from the corresponding behaviour of some small cations and anions in aqueous dimethyl sulphoxide (DMSO) and acetonitrile (ACN) solvents.